The method and apparatus of this invention are ones relating to the cutting of pattern pieces from sheet material by means of a cutting tool moved along lines of cut defining the pattern pieces and wherein as the cutting tool is moved along such a line of cut the cutting of the involved pattern piece is interrupted, the cutting tool is removed from cutting engagement with the material, and the material is advanced to bring a fresh segment of it to the cutting station before the cutting of the involved pattern piece is resumed.
After pattern pieces are cut from sheet material they are removed either by hand or by machine from the adjacent waste material. To allow an efficient separation it is quite important that the pattern pieces be cleanly cut from the waste material and that no uncut strings, threads or connecting bridges exist between the pieces and the waste material. If such uncut features exist the pattern pieces may fail to be removed or expensive time consuming additional manual steps may have to be performed to complete the separation. Further, the cut pattern pieces may have an irregular shape. One way to eliminate, or at least reduce, these problems is to cut each pattern piece with a single complete movement of the cutting tool along the periphery of each pattern piece without removing it from start to finish from cutting engagement with the material. Such "all-at-once" cutting of a pattern piece is not, however, always practical or possible and it may in many instances be desirable or necessary to interrupt the cutting of a pattern piece periphery with the cutting tool being withdrawn from cutting engagement with the material during such interruption. Unfortunately, the points at which these interruptions occur tend to be points at which irregularities or incomplete cutting of the pattern pieces from the waste material may occur.
Until recently, conveyorized cutting machines have been designed with cutting station lengths long enough to make it practical, if desired, to cut most or all of the wanted pattern pieces so that each is cut in a single continuous cycle of the cutting tool around its periphery. Typically, the cutting stations of these machines have been 13 to 20 feet or more in length. Since the cost of such a machine is directly proportional to its cutting station length a machine with a shorter cutting station can offer advantages of lower cost and of requiring less floor space. A shortened cutting station, however, may make it difficult or impossible to design cutting markers permitting each pattern piece to be cut all at once without shifting the material relative to the cutting station. That is, as the cutting station length is shortened it becomes more necessary to cut some pattern pieces in two or more stages with the work material being advanced between each stage. The points at which the periphery of such a pattern piece intersects the dividing line between adjacent segments of the material are points at which clean cutting problems are likely to occur due to shifting or mispositioning of the material taking place at such a point between the time of first cutting at that point and the time of later cutting at the same point.
When automatically cutting pattern pieces from a length of work material in accordance with a marker, marker information is supplied to the controller of the cutting machine in the form of data describing the peripheries of pattern pieces in terms of points identified by X and Y coordinates referenced to a set of X and Y marker coordinate axes. This marker data is then converted to machine commands, for controlling movement of the cutting tool in X and Y coordinate directions, defining the desired paths of movement of the cutting tool by points described by X and Y coordinates referenced to X and Y coordinate axes fixed relative to the machine frame. When the work material is initially placed on the supporting surface of the machine it takes a given positional relationship with respect to the machine coordinate axes. This initial positional relationship between the work material and the machine coordinate axes may, depending on circumstances, be established somewhat casually or with different degrees of care; however, for accurate cutting of the entire marker it has been necessary in the past that the positional relationship between the work material and the machine coordinate axes be maintained from start to finish in the cutting of the marker.
When cutting sheet material on a long non-conveyorized cutting machine few problems arise in keeping the work material fixed relative to the machine coordinate axes during the cutting of an entire marker. However, in conveyorized cutting machines problems do arise in that the material may shift relative to the machine coordinate axes during the segment-by-segment advances of the material to the cutting station, or in that the advancements themselves may be inaccruately carried out. In the cutting of the second and successive segments the material therefore may not be positioned where expected with regard to the machine coordinate axes, the cutting tool as a consequence following actual paths of movement on the work material displaced from the expected lines of cut. This displacement of the actual cut from the expected cut is particularly troublesome in cases where a pattern piece extends from one segment to another and may cause such a pattern piece to be of irregular shape or to be incompletely separated from the waste material in the vicinity of the points at which its periphery intersects the dividing line between the two segments.
The general object of the invention is therefore to provide a method and apparatus used in the automatic cutting of sheet material to overcome or reduce cutting problems arising from accidential shifting, flexural displacement or mispositioning of the work material relative to the coordinate axes of a cutting machine during advancement of the work material relative to the cutting station to bring a fresh segment of the material to the cutting station.
A more specific object of the invention is to provide a method and apparatus for promoting the regular and clean cutting of pattern pieces from work material in the segment-by-segment cutting of the work material in instances where pattern pieces extend from one segment to another.
Other objects and advantages of the invention will be apparent from the following detailed description of preferred embodiments of the invention and from the accompanying drawings and claims.